Networks of protein-protein interactions are the hallmarks of biological systems. Protein-protein interactions form signal pathways that regulate all aspects of cellular functions in normal and cancerous cells. Methods have been developed for detecting protein-protein interactions, such as transient receptor tyrosine kinase dimerization and complex formation after extracellular growth factor activation; however, these methods are not particularly designed to be used on formalin fixed paraffin embedded tissues.
A proximity ligation assay recently has been developed by OLink AB. This is the only known commercial product for in situ detection of protein-protein interactions on formalin fixed paraffin embedded tissue. Proximity ligation assay technology uses DNA ligases to generate a padlock circular DNA template, as well as Phi29 DNA polymerase for rolling circle amplification. These enzymes are expensive. Moreover, these enzymes are not amenable for use with automated systems and methods. For these reasons, proximity ligation assays are not considered generally useful for commercial applications.
As understanding disarrayed cellular pathway(s) becomes increasingly important to personalized diagnosis and treatment for cancer patients, in situ protein-protein detection in formalin fixed paraffin embedded tissue becomes an unmet medical need in tissue diagnosis.